Load clamping apparatus for lift trucks



' July 22, 1958 s. E. FARMER ETAL LOAD CLAMPING APPARATUS FOR LIFT 'mucxs 2 Sheets-Sheet 1 Filed Dec. 26. 1956 @444 W AH-bys.

y 1958 s. E. FARMER EIAL 2,844,403

LOAD CLAMPING APPARATUS FOR LIFT TRUCKS 2 Sheets-Sheet 2 Filed Dec. 26', 1956 INVENTORS S'f'anlcy' E. Farmer BY Harry]? WeinerZ' Hi2" s.

United States Patent LOAD CLAMPING APPARATUS FOR LIFT TRUCKS Stanley E. Farmer and Harry F. Weinert, Portland, 0reg., assignors to Cascade Manufacturing Company, Portland, 0reg., a corporation of Oregon Application December 26, 1956, Serial No. 630,557 3 Claims. (Cl. 29467) This invention relates to load clamping apparatus for lift trucks and more particularly to clamping apparatus which employs a pair of oppositely disposed pressure plate assemblies arranged to be moved toward each other thereby to apply pressure to the opposite side faces of an article or stack of articles located between the'pressure plate assemblies, enabling the articles to be lifted from the ground for handling.

In the transport of articles from one point to another, the advantages of employing clamping apparatus of-this type have long been recognized. Such clamping apparatus avoids the use of pallets and the accompanying capital outlay and upkeep costs which attend their use and, in most instances, permits faster and more expeditious handling of articles. Savings in storage space are also possible. This invention relates to an improvement in such clamping apparatus and has for its primary object the provision of a novel pressure plate assembly for such apparatus which is capable of applying pressure smoothly and evenly over a wide area of the side face of the load handled.

The problem of transmitting pressure evenly from the pressure plates of clamping apparatus to the load which the clamping apparatus engages has been the subject of a considerable amount of work. The suggestion has been made that each pressure plate assembly of the clamping apparatus employ a pair of pressure plates and that these plates be mounted in such a manner that each is permitted movement relative to the other when engaging the face of a load. Various constructions for mounting these plates have been proposed, including the arrangement wherein each plate is connected by a single pivot connection to a common support arm so that each of the plates is free to swing at any angle, either vertically or horizontally, relative to the common support arm. Such a construction is illustrated in United States Patent No. 2,681,- 162.

Known constructions employing a pair of pressure plates movably mounted on a common support arm have not been completely satisfactory, particularly when stacks of multiple cartons and relatively fragile articles are being handled. Inherent in the use of an extended plate through which pressure is transmitted by applying a force to one side of the plate is the occurrence of deflections and deformations in the plate. Bending of a plate away from a perpendicular plane is most severe in those areas of the plate which are spaced any extent from the point where force is applied to the plate. Commonly, pressure plates are mounted at a point somewhere near their center on a suitable support structure. Because of the deformations which occur, the amount of pressure exerted on the load by the outer extremities of the plates is considerably less than the pressure applied to the load by central portions, of the plates. Theplates, in effect, form modified arcs bending away at peripheral portions from the surface of the load engaged. When layers of' stacked goods are handled, this deformation is particularly troublesome, the lower layer of goods frequently tend- "ice ing, because of decreased pressure, to slide away and fall from the clamping apparatus. Similarly, the upper layers of goods, which are rather loosely held by the top portions of the plates, are easily joggled out of position.

Attempts have been made to control the inadvertent dropping or displacement of goods by either increasing the rigidity of the plates or using increased clamping pressures. The former alternative has the disadvantage of reducing the stability of the lift truck and increasing the cost of the apparatus, while the use of increased clamping pressures has resulted in destruction of intermediate layers of the goods.

Pressure plate assemblies which have employed a central pivot support for each plate in the assembly whereby the plates may swing angularly in any direction about their pivot supports are quite inadequate in handling relatively short stacks of goods, or skimming oif the top layers of a stack of goods. As soon as a plate assembly of this type engages a short stack of goods, the upper ends of the plates in the assembly are pivoted inwardly by reason of the lack of support existing adjacent these ends. This pivotal movement is accompanied by outward movement of the lower ends of the plates and a serious reduction in the clamping pressure exerted by these lower ends.

it is one of the objects of this invention to provide, in clamping apparatus for lift trucks, an improved pressure plate assembly wherein the pressure plates of the assembly are mounted on plural load arm members which are spaced from one another and so arranged that pressure is applied to the plates and thence to the load from spaced pressure points distributed over the surfaces of the plates.

Another object of this invention is to provide such a pressure plate assembly wherein the mountings between the pressure plates and load arms accommodate swinging movement of the plates about vertical axes and wherein the load arms are mounted on a support structure or arm base so that they may swing about a common axis parallel to these vertical axes, as required by the load.

Another object of this invention is to provide a pressure plate assembly of the hereinbefore described character wherein the connections between the plates and the spaced load arms, and the load arms and the support structure or arm base carrying the arms, comprise yieldable members flexibly supporting the various parts, the connections resiliently holding the pressure plates against a load when pressure is being applied from the pressure plates to a load.

Yet another object of the invention is to provide a pressure plate assembly having plural load arms pivotally supporting the plates of the assembly wherein the load arms are connected to the pressure plates by a series of pivot connections spaced at regular intervals upwardly from the bases of the pressure plates.

These and other objects and advantages are attained by the present invention, various novel features of which will become apparent as the following description is read in conjunction with the accompanying drawings wherein:

Fig. 1 is a side viewof a pressure plate assembly embodying this invention;

Fig. 2 is an end View of clamping apparatus for a lift truck showing a pair of laterally spaced pressure plate assemblies as they may be arranged on a lift truck for movement toward and away from each other for the purposes of gripping and releasing a load;

Figs. 3 and 4 are sectional views along the lines 3-3 and 4-4 in Fig. 1;

Fig. 5 is a top view of clamping apparatus employing 1 a pair of laterally spaced pressure plate assemblies; an

Fig. 6 is a perspective view of an hydraulically operated expansion-contraction mechanism such as may be used for mounting the pressure plate assemblies of this invention.

Clamping apparatus embodying this invention comprises, in general, a .pair of pressure plate assemblies affixed as by machine screws 11 to a pair of mounting plates 12 carried at opposite ends of an hydraulically operated expansion-contraction mechanism, indicated generally as 13. Mechanism 13 is of known construction and is adapted to be mounted on the usual lift mechanism carried at the forward end of the conventional lift truck with mounting plates 12 carried to either side of the lift truck. As illustrated, mechanism 13 has a pair of guide bars 16 and 17 associated with each of the mounting plates which are slidably mounted within a pair of cooperating guide tubes 18 and 19 for reciprocation back and forth within the guide tubes. The mechanism includes a double acting hydraulic motor 21 having a piston rod 22 connected to each of the mounting plates, actuation of the hydraulic motor serving to position the mounting plate associated therewith in expansion-contraction mechanism 13. Suitable means (not shown) are provided for regulating mechanism 13 and, in this manner, the lateral spacing of pressure plate assemblies 10.

Each pressure plate assembly 10 includes an arm base or mounting portion 25 having an inwardly projecting flange 26 extending vertically along its rear edge and a pair of vertically spaced suport projections 27 and 28 carried at its forward end. Arm base 25 is of relatively rigid construction and capable of delivering a substantial amount of pressure to the pressure plates of the assembly. Afl'lxed to the inner edge of each flange 26 are a number of U-shaped bars 29, and a bumper bar 31 which may take the form of a conventional channel member. Bars 29 and 31 are arranged along flange 26 so as to clear, yet pass closely adjacent, a similar set of bars carried by the companion pressure plate assembly. The bars are included to provide a support and restraining structure for the inner face of loads carried by the clamping apparatus.

Secured to each of the support projections 27, 28 is a load arm or butterfly member 36. The load arm members are bifurcated at each end, and each terminates at each of its ends in a pair of vertically spaced leg portions. The load arms are vertically spaced from one another and are connected intermediate their ends to the support projections of the arm base by vertically aligned pivot connections 37, 38.

Referring to Fig. 4, each pivot connection comprises a stud member or connecting pin 41, secured to the load arm as by welding, which projects outwardly through a loosely fitting bore 42 formed in the support projection of the arm base. A resilient member 43, such as a rubber pad, is placed between the load arm and arm base and encircling the stud member. Aflixed to the end of stud member 41 is a nut 44 and washer 46. The flexible pivot connection thus provided enables the load arms carried by each arm base 25 to pivot about a common vertical pivot axis. The flexible connection also accommodates a certain amount of relative displacement between each load arm and the arm base when force is transmitted from the arm base arm to the load arms while at the same time yieldably resisting this displacement. This is highly desirable since it has been discovered that a more uniform pressure may be created in the clamping mechanism if deformations between the various parts are taken care of in the pivot connections. In the embodiment illustrated, a series of bores are provided in each support projection so that the load arms may be adjusted longitudinally along the support projections. The butterfly construction of each load arm member which results in a pair of leg portions at each end spaced one from the other accommodates pivotal movement of the ends of the member into the vertical plane occupied by a support projection.

Each pressure plate assembly carries a pair of pressure plates 47, 48 connected to opposite ends, respectively, of each of the load arms of the assembly. Thus, the inner ends of each load arm are connected, as at 51, 52, 53, and 54, to pressure plate 47, and the outer ends of each load arm are connected, as at 56, 57, 58, and 59, to pressure plate 48. The connections for each plate are vertically aligned and accommodate swinging movement of the plate about a vertical axis parallel to the common pivot axis for the load arms. Each load arm is connected to each plate by a pair of pivot connections spaced substantially at equal distances above and below, respectively, the connection between the load arm and the arm base. The series of pivot connections connecting each plate to the load arms connect a portion of the pressure plate proximate the base of the plate and successive portions of the plate spaced at regular intervals upwardly therefrom. Thus, pressure is transmitted from the arm base and load arms to a load by means of pressure points distributed upwardly at regular intervals from base portions of the pressure plates.

As can be seen in Fig. 3, the connections between each plate and the load arms resemble the connections between the load arms and arm base. Each connection comprises, generally, a stud or connecting pin 61 aflixed to the pressure plate, a yieldable pad member 62 interposed between the pressure plate and load arm, and nut and washer assemblies 63. Longitudinal adjustment may be provided for by including a series of accommodating bores, as in the case of the connections between the load arms and arm base. The flexible connection provided by yieldable pad member 62 enhances the distribution of pressure from the load arms to the pressure plates by accommodating relative deformations and deflections between the two members while yieldably resisting the same.

Rubber sheets 66 are preferably afiixed to the inner faces of the pressure plates to increase the frictional grab of the plates when they engage a load.

By using the pressure plate assembly construction herein described, considerably larger loads may be handled for a given amount of force exerted by expansion-contraction mechanism 13 than was previously possible. The construction permits the pressure plates and load arms to swing about vertical axes as they seek to engage a load, the various connections between the arm base, load arms, and pressure plates being vertically aligned so as to allow this movement, Most important, structure has been included which insures that force is delivered to the pressure plates from a number of spaced pivot connection so that pressure is exerted on a load by the pressure plates from areas distributed evenly over the faces of the plates. The flexible connections discussed enhance the operation of the mechanism by taking care of relative displacements occurring between the various parts. Short or highly stacked loads may be handled with equal facility. Thus, in handling a short stack of articles,'the pivot connections proximate the bases of the plates serve to deliver force from the load arm base to lower portions of the plates while the pivot connections proximate the top of the plates restrain the top portions of the plates from unhindered movement inwardly over the top of the load. With a tall stack of articles, force is transmitted to the load through all the spaced pivot connections.

While there has been described a preferred embodiment of this invention, modifications may be made without departing from the scope of the invention, and it is desired to cover all modifications which would be apparent to one skilled in the art and that come within the scope of the appended claims.

It is claimed and desired 'to secure by Letters Patent:

-1. ,;In clamping apparatus .for a lift truck, a pressure plate assembly for applying pressure to the opposite sides of a load comprising an elongated upright arm base member having a pair of vertically spaced support projections projecting outwardly to one side thereof, said support projections occupying a common vertical plane, a pair of vertically spaced elongated load arm members arranged transversely of said am base member inwardly thereof, a pivot connection connecting one of said load arm members intermediate its ends to each of said support projections, the pivot connection accommodating pivotal movement of the load arm member about a vertical pivot axis, each of said load arm members terminating at each of its ends in a pair of vertically spaced leg portions located one above and one below the support projection mounting the load arm member, the spacing between the leg portions at each end of a load arm member enabling the load arm member to swing into the vertical plane occupied by the support projections, the pivot connection for one load arm member being vertically aligned with the pivot connection for the other load arm member, a pair of elongated upright pressure plates arranged sideby-side inwardly of said load arm members, and a pair of pivot connections connecting each of said pressure plates to one end of a leg portion of each of said load arm members, one of said pressure plates being connected to the adjacent legs of said load arm members and spaced to one side of the pivot connections between the load arm members and the arm base member, the other of said pressure plates being connected to the adjacent legs of said load arm members spaced to the other side of the pivot connections between the load members and the arm base member, the pivot connections for each pressure plate being vertically aligned and accommodating pivotal movement of the plate about a vertical axis, said pair of pivot connections between each pressure plate and one end of each load arm member comprising a pivot connection with each of the pair of leg portions at the end of the load arm member, each of said pivot connections including an elastic deformable seat thereby to allow limited rocking movement.

2. The clamping apparatus of claim 1 wherein each said seat comprises a yieldable pad member interposed etween and flexibly supporting a pressure plate relative to a load arm member.

3. The clamping apparatus of claim 1 wherein each said seat comprises a yielclable pad member interposed between and flexibly supporting a load arm member 20 relative to the arm base member.

References Cited in the file of this patent UNITED STATES PATENTS 

